The present invention relates to a cooling arrangement for a dynamoelectric machine; and, more specifically, the invention relates to a dynamoelectric machine with a cooling arrangement of the externally supplied liquid cooling type in which coolant is circulated in coolant passages associated with the heat generating portions of the machine.
JP-A-7-79544 (1995) discloses conventional externally supplied liquid cooling type dynamoelectric machine which was designed to provide an enhanced cooling effect. In this machine, coolant is caused to flow through coolant passages formed by a plurality of cooling tubes within a stator core, the cooling tubes being connected to form the coolant passages through which the stator core is directly cooled by the coolant.
However, machine have the following inherent problems. Namely, since the plurality of cooling tubes are connected using connecting tubes to constitute a single long coolant passage and the coolant has to flow through the long and narrow coolant passage with the help of a pump, a large pressure loss is caused in the coolant passage, the reduction of which is difficult.
Further, since the heat recovered from the coolant is generally used for a heater, for example, in a motor vehicle, it is desirable to limit the coolant temperature variation at the coolant outlet regardless of the magnitude of the generated heat from the dynamoelectric machine. However, in the conventional machine, no specific measures were taken which limit such coolant temperature variation at the coolant outlet, so that it was necessary to vary the coolant temperature at the inlet thereof depending upon the conditions, in order to maintain the coolant outlet temperature substantially constant regardless of the magnitude of generated heat from the dynamoelectric machine.
Still further, since cooling tubes made of electrically conductive material pass through the stationary core of the dynamoelectric machine, magnetic fluxes caused by the current flowing through the stationary windings of the stator core induce electromotive forces in the cooling tubes, and, as a result, electric circuits are formed between the stationary core and the cooling tubes which tend to deteriorate the output characteristic and efficiency of the dynamoelectric machine.